Toroidal Continuously Variable Transmissions (hereinafter generically referred to as “CVT”) are believed well known in the art. The operation of such a CVT will therefore only be briefly discussed herein.
Generally stated, a toroidal CVT is provided with a drive disk having a toroidal surface, a driven disk also having a toroidal surface facing the toroidal surface of the drive disk. Both disks being linked by rollers in contact with their respective toroidal surfaces. The angle of the rollers with respect to the drive and driven disks dictates the speed ratio between the driven and drive disks.
Often, toroidal CVTs are designed according to the so-called “dual cavity” configuration including two drive disks and a single driven disk having opposed toroidal surfaces and located between the two drive disks.
A clamping mechanism is conventionally used to bias the disks towards one another to therefore ensure that the rollers are adequately contacted by both the driving and the driven disks to thereby transfer torque therebetween. However, this clamping mechanism may cause premature wear of portions of the disks and rollers caused by vibrations to which the CVT may be subjected when the CVT is not in operation, for example during transport or maintenance thereof.
Indeed, while the CVT is in operation, a thin film of traction oil is present between the contacting surfaces of the rollers and disks. This film of oil is not maintained when the CVT is stopped or operated under low rotational speeds. Accordingly, when no oil film is present the metal-to-metal contact between the rollers and disks in conjunction with acting forces may cause damages in the form of scratches and other marks on both the disks and the rollers that may cause a premature wear of these surfaces. These forces may take the form of vibrations that occur during transportation (unit in a trailer while being transported over the road, railroad associated vibration or vibration occurring on a mobile application where the CVT is at rest while being moved from one site to another), when a unit is not operating but is positioned next to a vibration source such as an operating prime mover, or caused by the engine startup/shutdown torque spikes.
Generally speaking, the wear occurring during transport is going to be caused by fretting, which generates marks and scratches over the disk and roller surfaces and produces metallic debris. The metallic debris may enter the traction oil reservoir to thereby contaminate it and eventually cause more damages to be created on the rollers and disks. Furthermore, microstructural damage to the material may be caused, which is very difficult to detect.